The long-term aim of this work is to understand the molecular mechanisms of regulation of BK-type calcium (Ca2+)-activated potassium (K+) channels. BK channels are widely expressed among different cell types and exhibit significant functional diversity suited to their physiological roles. BK currents couple changes in sub membrane Ca2+ concentrations to changes in membrane potential and excitability. Activation of BK channels have been implicated in protection of neurons during ischemic attacks and regulation of BK channels by changes in oxidative conditions may have a profound impact on cellular electrical excitability. BK channels consist minimally of four pore-forming subunits. In addition, there are four auxiliary beta subunits, which differ not only in terms of tissue distribution, but also in terms of the functional properties of the resulting BK channels. Three beta subunits, the beta2, beta3, and beta4,are found in brain tissue, with beta4 being the most abundant brain subunit. The beta subunits account for much of the diversity of BK channel function among different tissues and, because of an abundance of cysteine residues in the 1betasubunit extracellular loop, may be an important potential target by which changes in oxidative conditions may alter BK channel function. Using methods of electrophysiology combined with molecular biology, this project will examine whether redox reactions involving cysteine residues of BK 1betasubunits particularly from brain may play an important role in modulating BK channel function in brain. First, the ability of redox reactions to influence the key functional roles of beta subunits, including inactivation, apparent Ca2+-dependence of gating, inward current rectification, and pharmacology will be examined. Second, the role of particular cysteine residues in these effects will be defined. Third, potential physiological mechanisms by which the redox conditions of key cysteines may be influenced will be tested. These studies will provide definitive information about molecular mechanisms that underlie the role of BK beta subunits in defining BK channel function and the role of redox reactions in regulation of channel function. BK channels are of broad importance in the normal functioning of a variety of excitable cells. Among different tissues, BK channels contribute to regulation of neuronal excitability, smooth muscle relaxation, synaptic transmission and hormone release. Furthermore, BK channels may play a key role as neuroprotectants during ischemic conditions. This work will provide important insight into the mechanisms by which this role of BK channels may occur.